The U.S.-led coalition is determined to disrupt the Islamic State group's oil trade, which earns Islamic State (IS) an estimated $10 million a week. But while the West is bombing oil trucks and facilities, Western countries also are indirectly buying the jihadists’ oil, admit Western diplomats.

Hours after Britain's House of Commons Wednesday approved a request by Prime Minister David Cameron to expand his country’s bombing campaign against the Islamic State to include targets in Syria, British warplanes struck at oil facilities controlled by the jihadists.

Fifty-six kilometers inside Syria's eastern border with Iraq, four British Tornado jets struck facilities in the Omar oilfield that help finance IS. Syrian monitoring groups say that other oil-related targets were struck by coalition warplanes this week.

In this photo made from video taken from Russian Defense Ministry official web site on Oct. 1, 2015, an aerial image of what they purport shows lines of oil trucks 14 km (8.8 miles) east of Dayr-az-Zawr, Syria.

The coalition has prioritized oil-related facilities and infrastructure as targets. It has avoided destroying oil fields themselves, however, fearing it would make the reconstruction of Syria after the war more difficult. Additionally, there are worries that bombing oilfields would create an environmental hazard.

In the past year, a coalition tally shows it has hit 260 oil-related targets.

Britain's defense minister, Michael Fallon, said the airstrikes are dealing a “very real blow at the oil and the revenue” on which IS depends.

Buying IS oil

The four-year multi-layered and highly complex conflict, though, has its twists and turns. Among them is the fact that Western governments are also helping to indirectly fund IS.

The West provides money to rebel militias and local groups inside rebel-controlled northern Syria who buy the oil they need from middlemen acting for IS.

“Most organizations are not sending fuel inside Syria; they are sending money. And guess who they are buying the fuel from?” asks Bassam al-Kuwaiti, a political activist based in southern Turkey who works closely with foreign and local non-profits, international relief organizations and for-profit development groups funded by the U.S. government and other Western powers.

“So are we serving the objective here?" he added. "But everybody is closing their eyes. Send fuel from here.”

FILE - In an image provided by the U.S. Air Force, an F-16 Fighting Falcon takes off from Incirlik Air Base, Turkey, Aug. 12, 2015, to launch airstrikes against Islamic State targets in Syria.

Several U.S. and European officials confirmed to VOA that oil is being bought from IS by Western-backed rebel militias, Syrian NGOs and the local councils that have emerged in insurgent-held areas in northern Syria. None was prepared to speak on the record.

International non-profits and for-profits would also prefer to overlook the oil purchases. "Do not write about this trade,” a senior German aid worker told VOA. “Don’t you dare. Relief groups inside need to do this to operate,” he said.

Western government officials and relief organizations argue there would be major logistical problems transporting oil into Syria from Turkey, especially with so many countries mounting airstrikes. Without oil and fuel, the rebellion against President Bashar al-Assad would collapse.

Oil blockade

In July, IS did impose a brief oil blockade on rebel-held northern Syria after it lost control of Tal Abyad, a key Syrian town on the Turkish border, to mainly Kurdish fighters.

While launching an offensive to the west of Tal Abyad on another border town, Azaz, IS ordered traders to stop trucking diesel and refined oil into rebel-held areas in northern Syria on threat of being beheaded.

The blockade affected more than just rebel fighters. The interdiction of fuel deepened the humanitarian crisis in northern Syria, disrupting everything from agriculture to medical clinics, which run on generators donated by Western countries. Bakeries, water supplies and aid deliveries were also badly impacted.

IS controls more than 10 oil fields in territory it holds. Revenue from trading in black gold helps the terror group run its claimed caliphate as well as a global terror network. The oil is sold to traders who then transport it to makeshift refineries or sell it on to smugglers for transport into Turkey.

Selling to Assad

Ironically, the Assad regime also has to buy IS oil to keep its war machine going.

Western and Iraqi officials were given a good rundown on the terror group’s oil trading with the Assad regime back in June 2014 when IS computers and databases were seized by Iraqi intelligence officers from the Mosul home of jihadist commander Abdulrahman al-Bilawi. The raid was conducted a few days before jihadists overran the northwestern Iraqi city.

The breakdown of the group’s financial resources shocked even senior Iraqi officials, who say the seized databases revealed IS was receiving cash not only from oil trafficking but also from selling to overseas traders, other Syrian insurgent groups and the Assad regime.